1. Field of the Invention
The present invention relates to a legged moving robot, and more particularly to an apparatus for recognizing the direction and position in which the foot of a movable leg of a legged moving robot is landed on a floor ridge, such as an edge of a stair or the like, with respect to the floor ridge.
2. Description of the Prior Art
When a legged moving robot such as a two-legged (biped) locomotion robot moves up or down a stair or on a rough surface, it is desirable to recognize the direction and position in which the foot of a movable leg of the legged moving robot is landed on a floor ridge, such as an edge of a stair or an upper surface of a floor convex, with respect to the floor ridge.
Specifically, when a biped locomotion robot ascends a stair with a certain gait (a walking pattern such as a stride), if the foot of one movable leg of the robot is landed on an edge of a stair step near the toe when the foot is to touch the stair step, then the foot of the other movable leg may possibly miss an upper stair step with the present gait when the other movable leg attempts to reach the upper stair step. Therefore, it is necessary to correct the gait of the robot, e.g., increase the stride.
Similarly, when the biped locomotion robot descends a stair with a certain gait, if the foot of one movable leg of the robot is landed on an edge of a stair step near the heel when the foot is to leave the stir step, then the foot of the movable leg may possibly miss a lower stair step with the present gait when the movable leg attempts to reach the lower stair step. Therefore, it is necessary to correct the gait of the robot, e.g., reduce the stride.
Furthermore, when a foot of a biped locomotion robot is landed on an edge of a stair while being oriented obliquely to the edge of t he stair upon ascent or descent along the stair, the robot tends to move obliquely up or down the stair with the present gait. Since the robot would otherwise possibly hit a lateral wall of the stair or the foot would otherwise possibly miss the stair, it is necessary to correct the direction in which to advance the feet of the robot.
For correcting the gait of the robot, it is desirable to recognize the direction and position in which the foot of the robot is landed on a floor ridge such as an edge of a stair, or the direction and position of a floor ridge with respect to the foot, when th e foot is landed on the floor ridge in line-to-line contact therewith.
One prior arrangement for recognizing the direction and position in which the foot of a robot is landed on an edge of a stair when the robot moves up or down the stair is disclosed in U.S. Pat. No. 5,737,217, for example.
According to the disclosed arrangement, a tape for reflecting light is applied to a stair step parallel to an edge thereof, and a plurality of light sensors that are longitudinal spaced are disposed on each of opposite sides of each of the robot feet. When a foot of the robot is landed on the stair step, the position and direction of the edge of the stair step with respect to the foot are recognized on the basis of which light sensor has detected the tape (those light sensors which are not positioned on the stair step do not detect the tape).
The tape applied to the stair step may comprise a metal sheet, and each of the light sensors on the robot feet may comprise an eddy-current proximity sensor. It is possible to recognize the position and direction of the edge of the stair step with respect to the foot by detecting the tape with the eddy-current proximity sensors.
However, since the tape needs to be applied to each of the stair steps, the robot is subject to limitations on ranges in which it can operate, and the overall system is relatively expensive. Furthermore, the light sensors tend to suffer erroneous detections due to smearing of the sensors or tapes and dirt attached to the sensors or tapes. As a result, it may often be impossible to properly recognize the position and direction of a stair edge with respect to the robot foot. Robots with eddy-current proximity sensors mounted on their feet are subject to limitations on ranges in which they can operate because these robots cannot walk on metallic stairs.
U.S. Pat. No. 5,255,753 discloses a robot having a distributed contact sensor which comprises a matrix of contact sensor elements mounted on each of the foot soles of a robot. The position and shape of a contact area on a foot sole of the robot can be detected from output data of the contact sensor elements. When a foot of the robot is landed on a stair step, the position and shape of a boundary between an area of the foot sole which is in contact with the stair step and an area of the foot sole which is out of contact with the stair step are recognized on the basis of output data of the contact sensor elements, for thereby recognizing the position and direction of the foot with respect to an edge of the stair step.
However, since the distributed contact sensor is mounted on the foot sole, the contact sensor is liable to be damaged due to impacts acting on the foot sole when the foot sole touches a floor during movement of the robot. If the contact sensor is covered with an elastic material such as rubber for protection against damage, then the contact sensor is unable to accurately detect the position and shape of a contact area of the foot sole. Furthermore, since many contact sensor elements are employed, a lot of processing operation is needed to process the output signals from the contact sensor elements.